Device for producing calibrating pulses



March 16, 1954 3 LE CQMTE DEVICE FOR PRODUCING CALIBRATING PULSES Filed NOV. 1, 1951 i i. v

INVENTOR Corsfiocm Le Comte gent Patented Mar. 16, 1954 DEVICE FOR PRODUCING CALIBRATING PULSES Corstiaan le Comte, Hilversum, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application November 1, 1951, Serial No. 254,231

Claims priority, application Netherlands November 9, 1950 4 Claims. 1

This invention relates to a device for producing calibrating pulses, particularly for the purpose of distance marking on image screens of radar devices.

Known devices of this kind comprise a resonant circuit connected in series with a grid-controlled, normally current-carrying electron tube, said resonant circuit (ringing circuit) being excited when a cut-off pulse is fed to the electron tube and then produces a damped oscillation in its natural frequency for the duration of the cutoff pulse.

. In order to compensate the decrease in ampli tude of the circuit voltage occurring while the rin ing circuit generates oscillations it is known to include the resonant circuit in a Hartley oscillator circuit arrangement or else to feed back a sinusoidal voltage from the resonant circuit in a different manner via an amplifier valve to the said resonant circuit.

The object of the invention is to provide a simplified device of the kind described for producing calibrating pulses having a high phase stability.

According to the invention, the ringing circuit alternating voltage controls a flip-flop circuit arrangement, adapted to produce in the output circuit output pulses coincident with zero passages of the ringing circuit voltage and suitable for calibration, a feedback coil coupled to the ringing circuit coil being also connected to the said output circuit for the supply of current pulses coincident with zero passages of the ringing circuit alternating voltage to the ringing circuit.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which Fig. 1 shows a circuit arrangement of a device according to the invention, and

Figures 2a to 2e show time diagrams to explain the operation of the device shown in Fig. 1.

Referring to Fig. 1, I designates a grid-controlled electron tube, th cathode lead of which includes a cathode resistor 3 shunted by a capacitor 2, whilst the anode of the tube is connected via a resonant or ringing circuit 4 comprising a coil 5, a parallel capacitor 6 and a damping resistor I, to a tapping 8 of an anode voltage source 9.

The tube I is normally current-carrying. If the control grid has a cut-ofi pulse of the kind denoted V1 in the voltage diagram shown in Fig.

. 2 2a supplied to it across terminals ID, the tube I is rapidly cut off.

Thus the resonant circuit 4 is excited and rings in its natural frequency for the duration of the cut-off pulse.

The damped oscillation thus set up at the ringing circuit 4, illustrated at V2 in Figure 2b (generally the duration of pulse V1 comprises a con siderably larger number of cycles of the ringing circuit frequency than shown) is fed to a flipflop circuit which comprises two grid-controlled electron tubes II and I2 having a common cathode resistor I3. The control-grid of tube II is connected to the anode of the normally current carrying tube I, whereas the control grid of tube I2 is connected on the one hand via a coupling capacitor It to the anode of the first tube I I and on the other via a grid resistor I '5 to the tapping 8 of the anode voltage source 9. The anode of the tube II is connected via an anode resistor I! to the anode voltage source 9.

This flip-flop circuit known per se has a stable and a meta-stable condition. In th stable or rest condition the tube I2 passes anode current and the tube II is cut-ofi. In the meta-stable condition the tube II passes anode current and the tube I2 is cut-off.

If we start with the above-described rest condition at the instant t:0, the grid of the tube II has fed to it a positive control voltage, the tube I I draws current and the voltage across the cathode resistor I3 increases, so that the tube I2 is cut off. The anode current thus occurring in the tube II brings about a reduction of the potential of the anode of this tube and this reduction in potential is transmitted by the capacitor I4 to the control grid of the tube I2, which, also due to the action of the voltages at the cathode resistor. results in the tube I2 being suddenly cut off and the tube II being simultaneously made conductive. The circuit thus flops over from the stable condition to the meta-stable condition.

This condition subsists for a time period which on the one hand is dependent on the periodicity of the sinusoidal voltage V2 supplied to the control grid of the tube II and on the other is dependent on the time constant of the flip-flop circult. This time constant mainly depends on the values of coupling capacitor I4, grid resistor I5 and anode resistor H.

In the meta-stable condition of the flip-flop circuit the potential of the control grid of tube I2 increases by the capacitor II becoming charged so that the control grid of tube I2 substantially reassumes its original potential within a half cycle of the sinusoidal voltage V2 that is to say approximately at the instant, at which V2 assumes a very steep slope and passes the zero axis in a negative direction. At this instant or thereabouts the cutting off of the tube [2 is removed and the circuit flips back from the metastable condition into the stable condition. At the subsequent zero passages of the alternating voltage V2 or thereabouts the cycle described is repeated. The variation of the voltage at the anode of the tube H and that of the voltage at the control grid of tube l2 are shown in Figures 20 and 2d respectively.

During the time the tube I2 is cut off a. rectangular current pulse is set up at its anode and is fed to a difierentiating network included in the anode circuit of the tube l2 and constituted by a coil I6 and a resistor H connected in parallel therewith. Periodically at the commencement and at the end of such a current pulse short pulses of positive and negative polarity respectively of the kind shown in Fig. 2c are set up across the differentiating network 'l5i'i, said pulses being coincident with zero passages of the ringing circuit voltageVz. These short voltage pulses are obtained across output terminals i8 and may be fed, if desired after amyplification and removal of the negative pulses, as calibrating pulses for example to the deflecting system of a cathode ray tube in radar devices.

The short pulses set up across the output circuit of the tube l2 and being coincident with the zero passages of the ringing circuit voltage V2 are fed to a feedback coil 9 connected in series with the differentiating network [6-1 I and give rise to feedback current pulses in the circuit A which are coincident with zero passages of the ringing circuit alternating voltage.

By the supply of a positive current pulse to the circuit at each zero passage in a positive direction of the circuit voltage and the supply of a negative current pulse at each zero passage in the negative direction'of the voltage V2, the decrease in amplitude of the ringing circuit voltage during the time the resonant circuit 4 rings is compensated each half cycle. Since the feedback current pulses only occur at the zero passages of the ringing circuit voltage V2 or thereab'outs the phase of the circuit alternating voltage is substantially not afiected. so that a particularly high phase stability of the calibrating pulses produced is obtained.

The anode circuit of the tube 1 includes a resistor 26 connected in series with the resonant circuit 4, said resistor constituting, together with the conductive tube l, a potentiometer for the obtainment of such a bias voltage at the control grid of the tube ii that when the tube l passes current the tube H remains cut off. The presence of the resistor 29 also governs the starting point of the flip-flop circuit, since when the tube 1 is cut-off the voltage across the resistor 26 (the voltage drop across the circuit 4 is comparatively low) is suddenly removed. The tube H of the flip-flop circuit then becomes rapidly conductive at the moment of time t:0.

in the circuit described the apices of the calibrating pulses, as may be seen from the time diagrams shown in Fig. 2, are not completely coincident with the zero passages of the sinusoidal voltage V2, but occur sooner by a time 1' which is small 'compared with a cycle T of the circuit voltage. 'The time 1- can be corrected by connecting a supplementary grid bias voltage source 2! in series with the grid. leak 15.

What I claim is:

1. Apparatus for generating calibrating pulses comprising an electron discharge tube having a control grid, a resonant circuit, means connecting said resonant circuit in series with said tube to a source of potential to produce a current flow in said tube, means to apply pulses to said grid to cut-ofi current flow in said tube whereby damped oscillations are developed across said resonant circuit, a flip-flop device coupled to said resonant circuit and responsive to said damped oscillations to produce pulses coincident with zero passages of said damped oscillations, and means coupled to said flip-flop device to feed back said pulses to said resonant circuit to maintain phase stability of the pulses yielded by said flip-flop device.

2. Apparatus for generating calibrating pulses comprising an electron discharge tube having a control grid, a resonant circuit, a source of direct potential, means connecting said tube in series with said resonant circuit across said source normally to produce current flow in said tube, means coupled to said grid to apply pulses to said tube to interrupt current fiow therein whereby said circuit is shock excited to produce damped oscillations, a hip-hop device coupled'to said resonant circuit and responsive to said dumped oscillations to produce pulses coincident with zero passages of said oscillations, and means including a coil coupling the device to said resonant circuit to feed back pulses to said resonant circuit to maintain phase stability of said pulses yielded by said device.

Apparatus for generating calibrating pulses, for purposes of distance marking on a radar screen, comprising an electron discharge switching tube having a cathode, a control grid and an anode, a resistor, a resonant circuit, a direct voltage source having its negative end connected to said cathode and its positive end connected through said resonant circuit in series with said resistor to said anode to produce a current flow in said tube, means to apply pulses to said grid to interrupt current flow in said tube whereby said circuit is shock excited to produce damped oscillations, a flip-fiop device coupled to said anode to produce pulses coincident with zero passages of said oscillations, and means including a coilcoupling said device to said resonant circuit to feed back pulses thereto to maintain phase stability of said pulses produced by said device.

4. Apparatus, as set forth in claim 3, wherein said flip-flop device is constituted by two electron discharge tubes each having a cathodefa grid and an anode, a common cathode resistor for said tube, a resistance, means applying a positive bias through said resistance to the grid of one tube normally to maintain current flow therein, a capacitor coupling the grid of said one tube to the anode of the other tube, and means connecting the grid of said other tube to the anode of said switching tube.

CORSTIAAN LE COMTE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,423,364 Fitch July 1, 1947 2,426,216 Hi'ght Aug. 26, 1947 2,438,904 De Rosa, Apr. 6, 1948 2,443,619 Hopper June 22, 1948 2,449,848 Hefele Sept. 21,1943 2,477,615 Isb'ister Aug. 2, 1949 2,495,704 De Rosa Jan. 31, 1950" 

